Multi-layer papermaker&#39;s forming fabric with auxiliary bottom md yarns

ABSTRACT

A papermaker&#39;s fabric includes a series of repeat units, wherein each of the repeat units includes: a set of top machine direction (MD) yarns having a first diameter; a set of bottom MD yarns having a second diameter larger than the first diameter; a set of auxiliary bottom MD yarns having the first diameter; a set of top cross machine direction (CMD) yarns interwoven with the top MD yarns to form a top fabric layer; a set of bottom CMD yarns interwoven with the bottom MD yarns and the auxiliary bottom MD yarns to form a bottom fabric layer; and a set of stitching yarns arranged in pairs, wherein at least one of the stitching yarns of the pair interweaves with the top and bottom fabric layers.

RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.16/268,932, filed Feb. 6, 2019, which claims priority from and thebenefit of U.S. Provisional Patent Application No. 62/629,348, filedFeb. 12, 2018. The disclosures of these prior applications are herebyincorporated herein by reference in full.

FIELD OF THE INVENTION

This application is directed generally to papermaking, and morespecifically to fabrics employed in papermaking.

BACKGROUND OF THE INVENTION

In the conventional fourdrinier papermaking process, a water slurry, orsuspension, of cellulosic fibers (known as the paper “stock”) is fedonto the top of the upper run of an endless belt of woven wire and/orsynthetic material that travels between two or more rolls. The belt,often referred to as a “forming fabric,” provides a papermaking surfaceon the upper surface of its upper run that operates as a filter toseparate the cellulosic fibers of the paper stock from the aqueousmedium, thereby forming a wet paper web. The aqueous medium drainsthrough mesh openings of the forming fabric, known as drainage holes, bygravity or vacuum located on the lower surface of the upper run (i.e.,the “machine side”) of the fabric.

After leaving the forming section, the paper web is transferred to apress section of the paper machine, where it is passed through the nipsof one or more pairs of pressure rollers covered with another fabric,typically referred to as a “press felt.” Pressure from the rollersremoves additional moisture from the web; the moisture removal isenhanced by the presence of a “batt” layer of the press felt. The paperis then transferred to a dryer section for further moisture removal.After drying, the paper is ready for secondary processing and packaging.

As used herein, the terms machine direction (“MD”) and cross machinedirection (“CMD”) refer, respectively, to a direction aligned with thedirection of travel of the papermakers' fabric on the papermakingmachine, and a direction parallel to the fabric surface and traverse tothe direction of travel. Likewise, directional references to thevertical relationship of the yarns in the fabric (e.g., above, below,top, bottom, beneath, etc.) assume that the papermaking surface of thefabric is the top of the fabric and the machine side surface of thefabric is the bottom of the fabric.

Typically, papermaker's fabrics are manufactured as endless belts by oneof two basic weaving techniques. In the first of these techniques,fabrics are flat woven by a flat weaving process, with their ends beingjoined to form an endless belt by any one of a number of well-knownjoining methods, such as dismantling and reweaving the ends together(commonly known as splicing), or sewing on a pin-seamable flap or aspecial foldback on each end, then reweaving these into pin-seamableloops. A number of auto joining machines are now commercially available,which for certain fabrics may be used to automate at least part of thejoining process. In a flat woven papermaker's fabric, the warp yarnsextend in the machine direction and the filling yarns extend in thecross machine direction.

In the second basic weaving technique, fabrics are woven directly in theform of a continuous belt with an endless weaving process. In theendless weaving process, the warp yarns extend in the cross machinedirection and the filling yarns extend in the machine direction. Bothweaving methods described hereinabove are well known in the art, and theterm “endless belt” as used herein refers to belts made by eithermethod.

Effective sheet and fiber support are important considerations inpapermaking, especially for the forming section of the papermakingmachine, where the wet web is initially formed. Additionally, theforming fabrics should exhibit good stability when they are run at highspeeds on the papermaking machines, and preferably are highly permeableto reduce the amount of water retained in the web when it is transferredto the press section of the paper machine. In both tissue and fine paperapplications (i.e., paper for use in quality printing, carbonizing,cigarettes, electrical condensers, and like) the papermaking surfacecomprises a very finely woven or fine wire mesh structure.

Typically, finely woven fabrics such as those used in fine paper andtissue applications include at least some relatively small diametermachine direction or cross machine direction yarns. Regrettably,however, such yarns tend to be delicate, leading to a short surface lifefor the fabric. Moreover, the use of smaller yarns can also adverselyaffect the mechanical stability of the fabric (especially in terms ofstretch resistance, skew resistance, narrowing propensity andstiffness), which may negatively impact both the service life and theperformance of the fabric.

To combat these problems associated with fine weave fabrics, multi-layerforming fabrics have been developed with fine-mesh yarns on the paperforming surface to facilitate paper formation and coarser-mesh yams onthe machine contact side to provide strength and durability. Forexample, fabrics have been constructed which employ one set of machinedirection yams which interweave with two sets of cross machine directionyarns to form a fabric having a fine paper forming surface and a moredurable machine side surface. These fabrics form part of a class offabrics which are generally referred to as “double layer” fabrics.Similarly, fabrics have been constructed which include two sets ofmachine direction yarns and two sets of cross machine direction yamsthat form a fine mesh paperside fabric layer and a separate, coarsermachine side fabric layer. In these fabrics, which are part of a classof fabrics generally referred to as “triple layer” fabrics, in the pastthe two fabric layers were typically bound together by separatestitching yams. However, today are more often bound together using yarnsfrom one or more of the sets of bottom and top cross machine directionand machine direction yams. As double and triple layer fabrics includeadditional sets of yarn as compared to single layer fabrics, thesefabrics typically have a higher “caliper” (i.e., they are thicker) thancomparable single layer fabrics. An illustrative double layer fabric isshown in U.S. Pat. No. 4,423,755 to Thompson, and illustrative triplelayer fabrics are shown in U.S. Pat. No. 4,501,303 to Osterberg, U.S.Pat. No. 5,152,326 to Vohringer, U.S. Pat. Nos. 5,437,315 and 5,967,195to Ward, and U.S. Pat. No. 6,745,797 to Troughton.

U.S. Pat. No. 5,967,195 to Ward discloses a triple layer fabric in whichpairs of stitching yams extend in the cross machine direction and formpart of the papermaking surface, in essence “completing the weave” ofthe papermaking surface, while also stitching with the bottom layer. Thefabrics disclosed in Ward have the same number of top machine directionyarns and bottom machine direction yarns. Such fabrics have proven toprovide an excellent papermaking surface (particularly due to theintegration of the stitching yarns into the weave of the papermakingsurface) and to combat inter-layer wear. U.S. Pat. No. 6,896,009 shows asimilar concept with MD stitching yarns.

Efficient drainage of water from a forming fabric can be an issue inpapermaking. One solution for efficient drainage is proposed inco-assigned U.S. Pat. No. 8,251,103 to Baumann, the disclosure of whichis hereby incorporated herein by reference. Baumann describes the use ofengineered channels formed by the interstices in the fabric to provideefficient drainage; the patent proposes the use of a calculated“drainage factor” and a “channel factor” to improve drainage efficiency.It would be desirable to provide additional fabrics that expand on thisconcept.

SUMMARY

As a first aspect, embodiments of the invention are directed to apapermaker's fabric comprising a series of repeat units, wherein each ofthe repeat units comprises: a set of top MD yarns having a firstdiameter; a set of bottom MD yarns having a second diameter larger thanthe first diameter; a set of auxiliary bottom MD yarns having the firstdiameter; a set of top CMD yarns interwoven with the top MD yarns toform a top fabric layer; a set of bottom CMD yarns interwoven with thebottom MD yarns and the auxiliary bottom MD yarns to form a bottomfabric layer; and a set of stitching yarns arranged in pairs, wherein atleast one of the stitching yarns of the pair interweaves with the topand bottom fabric layers.

As a second aspect, embodiments of the invention are directed to apapermaker's fabric comprising a series of repeat units, wherein each ofthe repeat units comprises: a set of top MD yarns; a set of bottom MDyarns; a set of auxiliary bottom MD yarns; a set of top CMD yarnsinterwoven with the top MD yarns to form a top fabric layer; a set ofbottom CMD yarns interwoven with the bottom MD yarns and the auxiliarybottom MD yarns to form a bottom fabric layer; and a set of stitchingyarns arranged in pairs, wherein at least one of the stitching yarns ofthe pair interweaves with the top and bottom fabric layers. Each of theauxiliary bottom MD yarns follows the same weaving sequence with thebottom CMD yarns as an adjacent bottom MD yarn.

As a third aspect, embodiments of the invention are directed to apapermaker's fabric comprising a series of repeat units. Each of therepeat units comprises: a set of top MD yams; a set of bottom MD yarns;a set of auxiliary bottom MD yams; a set of top CMD yams interwoven withthe top MD yams to form a top fabric layer; a set of bottom CMD yarnsinterwoven with the bottom MD yarns and the auxiliary bottom MD yarns toform a bottom fabric layer; and a set of stitching yarns arranged inpairs, wherein at least one of the stitching yams of the pairinterweaves with the top and bottom fabric layers. Each of the auxiliarybottom MD yarns is interwoven with the bottom CMD yarns such that itforms a knuckle under bottom CMD yarns under which the adjacent bottomMD yams also form knuckles.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a top view of a repeat unit of a papermaking forming fabricaccording to embodiments of the invention.

FIG. 2 is a bottom view of the fabric of FIG. 1.

FIG. 3 is a section view of a typical top CMD yarn of the fabric of FIG.1.

FIG. 4 is a section view of a typical pair of stitching yarns of thefabric of FIG. 1.

FIG. 5 is a section view of a typical bottom MD yarn of the fabric ofFIG. 1.

FIG. 6 is a top view of a repeat unit of a papermaking forming fabricaccording to embodiments of the invention.

FIG. 7 is a bottom view of the fabric of FIG. 6.

FIG. 8 is a section view of two typical top CMD yarns of the fabric ofFIG. 6.

FIG. 9 is a section view of a typical pair of stitching yarns of thefabric of FIG. 6.

FIG. 10 is a section view of a typical bottom MD yam and auxiliarybottom MD yam of the fabric of FIG. 6.

FIG. 11 is a top view of a repeat unit of a papermaking forming fabricaccording to embodiments of the invention.

FIG. 12 is a bottom view of the fabric of FIG. 11.

FIG. 13 is a section view of a typical top CMD yarn of the fabric ofFIG. 11.

FIG. 14 is a section view of a typical pair of stitching yarns of thefabric of FIG. 11.

FIG. 15 is a section view of a typical bottom MD yarn and auxiliarybottom MD yarn of the fabric of FIG. 11.

FIG. 16 is a graph plotting flow resistance as a function of fabricdepth for three different fabrics.

DETAILED DESCRIPTION

The present invention will now be described more fully hereinafter, inwhich embodiments of the invention are shown. This invention may,however, be embodied in different forms and should not be construed aslimited to the embodiments set forth herein. Rather, these embodimentsare provided so that this disclosure will be thorough and complete, andwill fully convey the scope of the invention to those skilled in theart. In the drawings, like numbers refer to like elements throughout.Thicknesses and dimensions of some components may be exaggerated forclarity.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof. As used herein the expression“and/or” includes any and all combinations of one or more of theassociated listed items.

In addition, spatially relative terms, such as “under”, “below”,“lower”, “over”, “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. It will beunderstood that the spatially relative terms are intended to encompassdifferent orientations of the device in use or operation in addition tothe orientation depicted in the figures. The device may be otherwiseoriented (rotated 90 degrees or at other orientations) and the spatiallyrelative descriptors used herein interpreted accordingly.

Well-known functions or constructions may not be described in detail forbrevity and/or clarity.

Referring now to the figures, a repeat unit of a papermaking formingfabric, designated broadly at 100, is shown in FIGS. 1-5. FIG. 1 showsthe paper side or “top” side of the fabric 100, and FIG. 2 shows themachine side of the fabric 100 (i.e., the side facing the papermakingmachine, referred to herein also as the “bottom” side of the fabric100).

FIG. 1 illustrates the top layer 102 of the fabric 100, which includestwelve top MD yarns 1-12, eight top CMD yarns 21-28, and eight stitchingyarn pairs 31 a, 31 b-38 a, 38 b, with a stitching yarn pair beinglocated between adjacent top CMD yarns. The top MD yarns 1-12, top CMDyarns 21-28 and stitching yarn pairs 31 a, 31 b-38 a, 38 b areinterwoven to form a plain weave surface on the top layer 102.

As can be seen in FIGS. 1 and 3, a typical top CMD yarn, such as top CMDyarn 21, follows an “over 1/under 1” sequence as it weaves with the topMD yarns 1-12. More specifically, top CMD yarn 21 passes over top MDyams 1, 3, 5, 7, 9 and 11 and under top MD yarns 2, 4, 6, 8, 10 and 12.Each of the other top CMD yarns 22-28 follows the same sequence.

As can be seen in FIGS. 1 and 4, corresponding pairs of stitching yarns31 a, 31 b-38 a, 38 b interweave with the top MD yarns and bottom MDyams in the following pattern. Each of the stitching yams of the repeatunit can be subdivided into two portions: a fiber support portion whichinterweaves with the top MD yarns, and a binding portion which passesbelow the top MD yarns and, in the illustrated embodiment, interweaveswith a bottom MD yarn. These are separated at “transitional” top MDyarns, below which one stitching yarn of a pair crosses the otherstitching yam of the pair. The stitching yarns of each pair areinterwoven relative to one another such that the fiber support portionof one yam of the pair is positioned above the binding portion of theother yarn of the pair. The fiber support portion of one stitching yarnof each pair interweaves in an alternating fashion with five top MDyarns (alternately passing over three top MD yarns and under two top MDyarns), and the fiber support portion of the other yam of the pairpasses over three other top MD yarns of the repeat unit while passingbelow two other top MD yarns positioned between those three top MDyarns. Both of the stitching yarns pass below the transitional top MDyarns. Thus, together the stitching yarns of each pair pass over six topMD yarns and under six top MD yarns in an “over 1/under 1” patternsimilar to that of the top CMD yarns.

As exemplified in FIG. 4 by stitching yarn pair 32 a, 32 b, eachstitching yarn interweaves with five top MD yarns (passing inalternating fashion over three top MD yarns and under two top MD yarns)and passes under one bottom MD yarn. For example, stitching yarn 32 apasses over top MD yarns 2, 4 and 6 and under top MD yarns 3 and 5 (andalso passes under bottom MD yarn 46, as discussed below), whilestitching yarn 32 b passes over top MD yarns 8, 10 and 12 and underbottom MD yarns 9 and 11. Thus, together the stitching yarns 32 a, 32 b(and each other pair of stitching yarns) form the equivalent of one topCMD yarn that weaves in the “over 1/under 1” sequence followed by thetop CMD yarns. As a result, together the top MD yarns 1-12, the top CMDyarns 21-28, and the portions of the stitching yarns 31 a, 31 b-38 a, 38b that weave with the top MD yarns form a plain weave surface for thetop layer 102. Such top surface constructions are well-known(exemplified in, for example, U.S. Pat. No. 5,967, 195 to Ward, thedisclosure of which is hereby incorporated herein) and need not bedescribed in detail herein.

Referring now to FIG. 2, the machine side of the fabric 100 includeseight bottom MD yarns 41-48, four auxiliary bottom MD yarns 42 a, 44 a,46 a, 48 a, and eight bottom CMD yarns 51-58 that form a bottom layer101. By way of explanation, the auxiliary bottom MID yarns 42 a, 44 a,46 a, 48 a (which are similar in size to the top MD yarns 1-12 andtherefore are smaller than the bottom MD yarns 41-48) are each pairedwith a respective bottom MD yarn 42, 44, 46, 48 and weave in the samepattern as that paired yarn. The bottom MD yarns 41-48 and the auxiliarybottom MD yarns 42 a, 44 a, 46 a, 48 a are interwoven with the bottomCMD yarns 51-58 in an “over 3/under 1/over3/under 1” sequence (forreference purposes, herein the terms “over” and “under” are used withrespect to the paper side of the fabric 10 being “up” and the machineside being “down”, as is shown in FIGS. 1 and 3-5, with theunderstanding that in the bottom view of FIG. 2, yarns seen as passing“over” other yarns actually pass “under” those yarns with the paper sidechosen as being “up”). For example, bottom MD yarn 44 passes over bottomCMD yarns 51-53, under bottom CMD yarn 54, over bottom CMD yarns 55-57and under bottom CMD yarn 58. The auxiliary bottom MD yarns 42 a, 44 a,46 a, 48 a weave identically to bottom MD yarns 42, 44, 46, 48respectively.

Referring now to FIGS. 2 and 5, each bottom MD yarn is offset from itsimmediate bottom MID yarn neighbors to create a 4-harness broken twillpattern on the bottom surface with the “knuckles” formed by the bottomMD yams. For example, bottom MD yarn 41 passes under bottom CMD yams 52and 56, bottom MD yarn 42 passes under bottom CMD yarns 53 and 57,bottom MD yarn 43 passes under bottom CMD yams 51 and 55, and bottom MDyarn 44 passes under bottom CMD yarns 54 and 58. The remaining bottom MDyarns 45-48 follow a similar offset pattern (see FIG. 2).

The bottom layer 101 also includes knuckles formed by the stitchingyarns 31 a, 31 b-38 a, 38 b under the bottom MD yarns 41-48 andauxiliary bottom MD yams 42 a, 44 a, 46 a, 48 a. The knuckles form a4-harness broken twill pattern. As examples, the stitching yarns 31 a,31 b form knuckles under bottom MD yarns 41, 45, the stitching yarns 32a, 32 b form knuckles under bottom MD yarns 42, 46 (as well as underauxiliary bottom MD yarns 42 a, 46 a), the stitching yams 33 a, 33 bform knuckles under bottom MD yams 44, 48 (as well as under auxiliarybottom MD yarns 44 a, 48 a), and the stitching yarns 34 a, 34 b formknuckles under bottom MD yarns 43, 47. A similar pattern is repeated forstitching yarns 35 a, 35 b-38 a, 38 b (see FIGS. 2 and 4).

Those skilled in this art will appreciate that, although the stitchingyarns 31 a, 31 b-38 a, 38 b are woven with both stitching yarns of thepair both weaving with the top MD yams and stitching under the bottom MDyarns, in some embodiments only one stitching yarn of the pair maystitch under the bottom MD yams, with the other stitching yarn of thepair simply routed between the top and bottom MD yarns instead ofstitching. This so-called “phantom” stitching yarn is described, forexample, in U.S. Pat. No. 7,931,051 to Ward, the disclosure of which ishereby incorporated by reference herein in its entirety.

Turning now to FIGS. 6-10, a repeat unit of a forming fabric accordingto embodiments of the present invention, designated broadly at 200, isillustrated therein. The repeat unit 200 includes twelve top MD yarns201-212, eight top CMD yarns 221-228, four pairs of stitching yarns 231a, 231 b-234 a, 234 b, eight bottom MD yarns 241-248, four auxiliarybottom MID yams 241 a, 243 a, 245 a, 247 a, and eight bottom CMD yarns251-258. The interweaving of these yarns is described below.

Turning first to FIG. 6, the top surface of the fabric 200 is showntherein. The top CMD yarns 221-228 and stitching yarns 231 a, 231 b-234a, 234 b are arranged in an alternating pattern in which two top CMDyarns are followed by a pair of stitching yarns. As exemplified in FIG.6, top CMD yarns 221 and 222 follow stitching yarn pair 231 a, 231 b,then stitching yarn pair 232 a, 232 b follows top CMD yam 222. Thispattern of “stitching yarn pair/two top CMD yarns ” continues throughoutthe repeat unit.

Each of the top CMD yarns 221-228 interweaves with the top MD yarns inan “over 1/under 1” sequence. Because two top CMD yarns are positionedbetween a pair of stitching yams, they pass over alternating top MDyarns. This pattern is shown in FIG. 8, wherein top CMD yarn 222 isshown passing over top MD yarns 202, 204, 206, 208, 210 and 212, whereastop CMD yarn 221 is shown passing over top MD yams 201, 203, 205, 207,209 and 211.

In its fiber support portion, each stitching yarn 231 a, 231 b-234 a,234 b passes over top MD yarns that the adjacent top CMD yarns passbeneath and under the top MD yarns that the adjacent top CMD yarns passover. For example, and as shown in FIG. 9, the fiber support portion ofstitching yarn 232 a passes over top MD yarns 201, 203 and 205 whilepassing under top MD yarns 202 and 204, and stitching yam 232 b passesover top MD yarns 207, 209 and 211 while passing below top MD yarns 208and 210. Both stitching yarns 232 a, 232 b pass below the transitionaltop MD yarns 206, 212. The remaining stitching yarn pairs weave in asimilar manner, although they are offset from adjacent stitching yarnpairs by three top MD yarns. In this manner, the stitching yarns 231 a,231 b-234 a, 234 b and the top CMD yarns 221-228 form a plain weavepattern with the top MD yams 201-212 (see FIG. 6).

Turning now to FIGS. 7 and 10, the bottom surface of the fabric is showntherein. The bottom MD yarns 241-248 interweave with the bottom CMDyarns 251-258 in an “over7/under 1” pattern” (note that FIG. 7 is abottom view of the fabric 200 and is opposite the view of FIG. 6, so thedescription of the bottom MD yarns passing “over 4” bottom CMD yams isconsistent with the “over” and “under” conventions adopted with respectto FIGS. 6 and 8-10 rather than the view seen in FIG. 9). For example,bottom MD yarn 241 passes over bottom CMD yams 251 and 252, under bottomCMD yarn 253, and over bottom CMD yams 254-258 (see FIG. 10). Theremaining bottom MD yarns follow a similar pattern, with each bottom MDyarn being offset from its adjacent bottom MD yarns in a double brokentwill pattern.

The auxiliary bottom MD yarns 241 a, 243 a, 245 a, 247 a are woven withthe bottom CMD yams 251-258 in either an “over 5/under 1/over 1/under 1”sequence or an “over 2/under 1/over 4/under 1” sequence. Each “under 1”knuckle of the auxiliary bottom MD yarns aligns with the “under 1”knuckles of the bottom MD yarns that sandwich that auxiliary bottom MDyam. For example, auxiliary bottom MD yarn 241 a forms knuckles underbottom CMD yarns 251, 253, which are the same bottom CMD yarns underwhich bottom MD yarns 241, 242 (located on either side of auxiliarybottom MD yarn 241 a) form knuckles (see FIG. 10). The remainingauxiliary bottom MD yams similarly form knuckles aligned with theirneighboring bottom MD yarns.

Also, the binding portion of each of the stitching yarns 231 a, 231b-234 a, 234 b is stitched below two bottom MD yarns, with the stitchingyarns of a pair stitching below bottom MD yarns that are separated bytwo bottom MD yarns. For example, as shown in FIG. 9, stitching yarn 232a passes below bottom MD yams 246 and 247, and stitching yarn 232 bpasses under bottom MD yarns 242, 243. Adjacent pairs of stitching yarnsare offset from each other by two bottom MID yarns.

Turning now to FIGS. 11-15, a repeat unit of a forming fabric accordingto embodiments of the present invention, designated broadly at 300, isillustrated therein. The repeat unit 300 includes twelve top MD yarns301-312, six top CMD yarns 321-326, four pairs of stitching yarns 331 a,331 b-334 a, 334 b, eight bottom MD yarns 341-348, four auxiliary bottomMD yarns 342 a, 344 a, 346 a, 348 a, and four bottom CMD yarns 351-354.The interweaving of these yams is described below.

Turning first to FIG. 11, the top surface of the fabric 300 is showntherein. The top CMD yarns 321-326 and stitching yarns 331 a, 331 b-334a, 334 b are arranged in a pattern in which one top CMD yarn is followedby a pair of stitching yarns, then two top CMD yarns are followed byanother pair of stitching yarns. As exemplified in FIG. 11, top CMDyarns 321 is followed by stitching yarn pair 331 a, 331 b, then two topCMD yarns 322, 323 are followed by stitching yarn pair 332 a, 332 b.This pattern of “one top CMD yarn/stitching yarn pair/two top CMDyarns/stitching yarn pair” continues throughout the repeat unit.

Each of the top CMD yarns 321-326 interweaves with the top MD yams in an“over 1/under 1” sequence. This pattern is shown in FIG. 13, wherein topCMD yarn 321 is shown passing over top MD yams 301, 303, 305, 307, 309,311 and under top MD yams 302, 304, 306, 308, 310 and 312.

In its fiber support portion, each stitching yarn 331 a, 331 b-334 a,334 b passes over top MD yarns that the adjacent top CMD yarns passbeneath and under the top MD yarns that the adjacent top CMD yarns passover. For example, and as shown in FIG. 14, the fiber support portion ofstitching yarn 331 a passes over top MD yarns 302, 310 and 312 whilepassing under top MD yarns 301 and 311, and stitching yarn 331 b passesover top MD yarns 304, 306 and 308 while passing below top MD yarns 305and 307. Both stitching yarns 331 a, 331 b pass below the transitionaltop MD yarns 303, 309. The remaining stitching yarn pairs weave in asimilar manner, although they are offset from adjacent stitching yarnpairs in a double broken twill pattern. In this manner, the stitchingyams 331 a, 331 b-334 a, 334 b and the top CMD yarns 321-326 form aplain weave pattern with the top MD yarns 301-312 (see FIG. 11).

Turning now to FIGS. 12 and 15, the bottom surface of the fabric isshown therein. The bottom MD yams 341-348 interweave with the bottom CMDyarns 351-354 in an “over 3/under 1” pattern” (note that FIG. 12 is abottom view of the fabric 300 and is opposite the view of FIG. 11, sothe description of the bottom MD yams passing “over 4” bottom CMD yarnsis consistent with the “over” and “under” conventions adopted withrespect to FIGS. 11 and 13-15 rather than the view seen in FIG. 12). Forexample, bottom MD yarn 342 passes over bottom CMD yarns 351-353 andunder bottom CMD yarn 354 (see FIG. 15). The remaining bottom MD yarnsfollow a similar pattern, with each bottom MD yarn being offset from itsadjacent bottom MD yarns in a double broken twill pattern.

The auxiliary bottom MD yams 342 a, 344 a, 346 a, 348 a are woven withthe bottom CMD yarns 351-354 in an “over 3/under 1” sequence. Each“under 1” knuckle of the auxiliary bottom MD yarns aligns with the“under 1” knuckle of a paired adjacent bottom MD yarn. For example,auxiliary bottom MD yarn 342 a forms a knuckle under bottom CMD yams352, which are the same bottom CMD yarn under which paired bottom MDyarn 342 forms a knuckle (see FIG. 15). The remaining auxiliary bottomMD yarns similarly form knuckles aligned with their adjacent bottom MDyams.

Also, the binding portion of each of the stitching yarns 331 a, 331b-334 a, 334 b is stitched below one bottom MD yarn, with the stitchingyarns of a pair stitching below bottom MD yarns that are separated bythree bottom MD yarns. For example, as shown in FIG. 14, stitching yarn331 a passes below bottom MD yarn 348 (and auxiliary bottom MD yarn 348a), and stitching yarn 331 b passes under bottom MD yam 344 (andauxiliary bottom MD yarn 344 a). Adjacent pairs of stitching yams areoffset from each other in a double broken twill pattern.

Those of skill in this art will recognize that the total of six top CMDyams, four CMD stitching yam pairs, and four bottom CMD yarns forms a5:2 ratio of effective top CMD yarns (i.e., number of top CMDyarns+number of stitching yarn pairs) to bottom CMD yarns (i.e., numberof bottom CMD yarns). This ratio, which is discussed in, for example,U.S. Pat. No. 8,196,613 to Ward, can provide fabrics with an excellentbalance of properties including permeability, fiber support, stabilityand wear volume. In particular, CMD fiber support may be improved overfabrics with a 2:1 ratio because there are more top CMD yarns per inch.In some embodiments a 5:3 ratio may also be employed.

Those skilled in this art will appreciate that yarns of different sizesmay be employed in fabric embodiments of the present invention. Forexample, the top MD yarns, top CMD yarns, auxiliary bottom MD yarns, andstitching yarns may have a diameter of between about 0.10 and 0.20 mm,the bottom MD yarns may have a diameter of between about 0.18 and 0.40mm, and the bottom CMD yarns may have a diameter of between about 0.20and 0.50 mm. The mesh of fabrics according to embodiments of the presentinvention may also vary. For example, the mesh of the top surface mayvary from about 20×30 to 30×50 (epcm to ppcm), and the total mesh mayvary between about 60×45 to 90×75. More specifically, yarns for thefabrics 100, 200 may be selected as set forth in Table 1:

TABLE 1 Yarn type Size (mm) Top MD Yarn 0.16 Top CMD Yarn 0.17 CMDStitching Yarns 0.19 Bottom MD Yarns 0.34 Auxiliary Bottom MD Yarns 0.16Bottom CMD Yarns 0.48

Parameters of a specific embodiment of the fabric 300 of FIGS. 11-15 areset forth in Table 2.

TABLE 2 Property XTD-775 Weave Pattern: 1 × 1/4HS Yarn Ratios (md ×cmd): 1:1 (special) × 5:2 MD Sizes (mm):  .16/.34 CD Sizes (mm):.17/.19/.48 PS Mesh (epi × ppi): 55 × 62 PS Mesh (epcm × ppcm): 21.7 ×26.0 Permeability (cfm): 450 MD Fiber Support Index: 36 CD Fiber SupportIndex: 83 Total Fiber Support Index: 119 Top Open Area (%): 37.0 Caliper(mm): 1.20 GB Stretch (%): 0.29 Delta 100 (%): 0.62 Burial (mm): 0.243Skew (mm): 24 Wear Volume (mm³/cm²): 9.7 CMD Stiffness (TSU): 153

The weave patterns of fabrics 100, 200, 300 can create engineereddrainage channels of the type described in Baumann, supra, and can do soin fabrics with more yarns having the size of top MD yams (Le., eithertop MD yarns or auxiliary bottom MD yarns) than main bottom MD yarns.Doing so can reduce the paper-side MD yarn count relative to themachine-side MD yarn count (while maintaining or increasing thepaper-side CMD yarn count), thereby increasing the paper-side open areaand reducing the machine-side open area to the extent that the drainagechannels become more like as described in Baumann—which can improvefabric drainage. As an example, FIG. 16 is a graph showing the flowpressure across the thickness of the fabric. The line labeled “Fabric 3”represents the fabric of FIGS. 11-15 and demonstrates reduced drainagepressure on both the paper side and the machine side of the fabriccompared to similar prior fabrics. Also, flow velocity is reduced on thepaper side of the fabric.

Also, increased paper-side open area without reducing the paper-side CMDyarn count and/or CMD yarn diameters can maintain or improve surface andinternal wear. It improves fabric stability and seam strength potentialparticularly with long float bottom weaves. It can also significantlyincrease the design flexibility for MD yams with paper-side tomachine-side MD yarn ratios greater than one.

The form of the yarns utilized in fabrics of the present invention canvary, depending upon the desired properties of the final papermaker'sfabric. For example, the yarns may be monofilament yarns, flattenedmonofilament yams as described above, multifilament yarns, twistedmultifilament or monofilament yarns, spun yarns, or any combinationthereof. Also, the materials comprising yarns employed in the fabric ofthe present invention may be those commonly used in papermaker's fabric.For example, the yams may be formed of polyester, polyamide (nylon),polyurethane, polypropylene, aramid, or the like. The skilled artisanshould select a yam material according to the particular application ofthe final fabric. In particular, round monofilament yams formed ofpolyester or polyamide may be suitable, and, as noted, the use ofmonofilament yarns as bottom MD yarns may be particularly suitable.

Although each of the embodiments includes a plain weave top surface,other embodiments may include a top surface having a different weavepattern, including twill, satin, or the like. In addition, the bottomsurfaces of the fabrics may take other weave patterns, including satin,twill or the like. Also, additional weave patterns with differentnumbers and ratios of top and bottom MD and CMD yams may also benefitfrom the concepts discussed herein. Further, in some embodiments thestitching yarns may be MD stitching yams rather than CMD stitching yams.

Pursuant to another aspect of the present invention, methods of makingpaper are provided. Pursuant to these methods, one of the exemplarypapermaker's forming fabrics described herein is provided, and paper isthen made by applying paper stock to the forming fabric and by thenremoving moisture from the paper stock. As the details of how the paperstock is applied to the forming fabric and how moisture is removed fromthe paper stock is well understood by those of skill in the art,additional details regarding this aspect of the present invention neednot be provided herein.

The foregoing embodiments are illustrative of the present invention, andare not to be construed as limiting thereof. Although exemplaryembodiments of this invention have been described, those skilled in theart will readily appreciate that many modifications are possible in theexemplary embodiments without materially departing from the novelteachings and advantages of this invention. Accordingly, all suchmodifications are intended to be included within the scope of thisinvention as defined in the claims. The invention is defined by thefollowing claims, with equivalents of the claims to be included therein.

That which is claimed is:
 1. A papermaker's fabric, comprising a seriesof repeat units, each of the repeat units comprising: a set of topmachine direction (MD) yarns having a first diameter; a set of bottom MDyarns having a second diameter larger than the first diameter; a set ofauxiliary bottom MD yams having the first diameter; a set of top crossmachine direction (CMD) yarns interwoven with the top MD yarns to form atop fabric layer; a set of bottom CMD yams interwoven with the bottom MDyarns and the auxiliary bottom MD yarns to form a bottom fabric layer;and a set of stitching yarns arranged in pairs, wherein at least one ofthe stitching yarns of the pair interweaves with the top and bottomfabric layers.
 2. The papermaker's fabric defined in claim 1, whereineach of the auxiliary bottom MD yarns follows the same weaving sequencewith the bottom CMD yarns as an adjacent bottom MD yarn.
 3. Thepapermaker's fabric defined in claim 1, wherein each of the auxiliarybottom MD yarns is interwoven with the bottom CMD yarns such that itforms a knuckle under bottom CMD yarns under which immediately adjacentbottom MD yarns also form knuckles.
 4. The papermaker's fabric definedin claim 1, wherein the top MD yarns, the top CMD yarns, and thestitching yarns form a plain weave surface.
 5. The papermaker's fabricdefined in claim 1, wherein the stitching yarns are CMD stitching yarns.6. The papermaker's fabric defined in claim 1, wherein the number of topMD yarns is equal to the sum of the number of bottom MD yarns and thenumber of auxiliary bottom MD yarns.
 7. The papermaker's fabric definedin claim 1, comprising equal numbers of top CMD yarns and stitching yarnpairs.
 8. The papermaker's fabric defined in claim 1, comprising twiceas many top CMD yarns as stitching yarn pairs.
 9. The papermaker'sfabric defined in claim 1, wherein a ratio of (a) top CMD yarns andstitching yarn pairs to (b) bottom CMD yarns is 5:2.
 10. Thepapermaker's fabric defined in claim 1, wherein both of the yarns ofeach stitching yarn pair stitch with the bottom MD yarns.